DNS server can't be reached on phone

[JoannaPerez]

I have this problem, my modem was changed by two techs yesterday because of connection problem, when I tried to search for the sites that I usually visit on my pc (like wikipedia, mangago, etc.), it always says that dns server can't be reached or something, it also happens on my mobile phones (android and iphone) then I tried to do a tutorial in youtube on how to solve this problem and it works on my pc, I just did it now. but the problem on my phone is still the same, I can't load some pages, I tried to search these sites using my cousin's phone and it works perfectly fine on her but not on mine. Please help me to solve this and what's the cause of this?

 

[DelJo63]

Go to settings, WiFi and FORGET your current SSID. Power off the phone and then restart it.
Finally, go back to settings->WiFi and reselect your router SSID.

 

[JoannaPerez]

Go to settings, WiFi and FORGET your current SSID. Power off the phone and then restart it.
Finally, go back to settings->WiFi and reselect your router SSID.

it still doesn't work, I tried searching on my iphone using google and safari but it only says that webpage is not available, while on my android it only says server dns address could not be found.